In third generation cellular systems (3GPP), where UMTS FDD and UMTS-TDD spectra are both allocated, continuous (FDD) and discontinuous (TDD) transmissions are employed. In FDD mode, transmissions are continuous because each transmission is associated with a particular code and frequency. In TDD mode, the transmissions are discontinuous because each transmission is associated with not only a particular code and frequency but also a particular time slot. The uplink and downlink transmissions share the same frequency which is divided into time slots, with some time slots being used for the downlink and some time slots being used for the uplink. In 3GPP, an uplink is defined as the frequency at which a wireless transmit/receive unit (WTRU) transmits and a base station (BS) receives; and the downlink is defined as the frequency at which a BS transmits and a WTRU receives.
In FDD mode, transmissions may occur in A-bands and B-bands. The FDD A-band uplink range is 1920 to 1980 MHz while the downlink range is 2110 to 2170 MHz. The B-band uplink range is 1850 to 1910 MHz while the downlink range is 1930 to 1990 MHz. In TDD mode, transmissions may occur in A-, B-, and C-bands. The TDD A-band is 1900 to 1920 MHz and 2010 to 2025 MHz. The B-band is 1850 to 1910 MHz and 1930 to 1990 MHz. The C-band spans 1910 to 1930 MHz. It should be noted that the particular bands and frequencies identified in this paragraph may vary according to system deployment and are mentioned purely for example to illustrate that FDD and TDD bands may be adjacent to each other in certain cases.
Since the uplink bands of the FDD spectrum may be adjacent to TDD bands, TDD WTRUs and TDD BSs may experience not only discontinuous interference from the discontinuous transmissions of other TDD WTRUs and BSs but also continuous interference from the continuous transmissions of FDD WTRUs and BSs. The interference usually causes loss of signal strength resulting invariably in poor performance to the TDD user that is subject to the interference.
It would therefore be desirable to determine appropriate escape mechanisms and control interference in coexisting TDD/CDMA (UMTS) and FDD/CDMA (UMTS) systems.